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A suicide bomber disguised as a mourner killed at least 22 people inside a Shia Muslim mosque in northern Iraq Wednesday when he detonated his explosives in the middle of a crowded funeral ceremony.

The attack on a religious target came as Shia Prime Minister Nouri al-Maliki faces pressure from mass Sunni protests that are worsening fears that Iraq could slide back into widespread sectarian confrontation.

Dressed in a suit, the bomber mingled with mourners before the blast at the Saif al-Shuhada — Sword of the Martyrs — Mosque in Tuz Khurmato city at a ceremony for a Shia ethnic Turkman, police and witnesses said.

"I was sitting in the seats at the back when all of sudden I heard the sound of a huge explosion. Thank God I was behind because people in front of me saved me with their bodies," said Abbas Qadir Mohamed, 35, one of the wounded.

Rigot Mohamed, an Iraqi army spokesperson, said at least 22 people were killed and more than 50 wounded in the blast in the religiously and ethnically mixed city 170 km north of the capital Baghdad.

No one claimed responsibility, but Al-Qaeda's local wing, Islamic State of Iraq, often targets Shia Muslim pilgrims and sites to try to trigger the kind of Shia-Sunni confrontation that killed thousands in 2006–2007 in Iraq.

Maliki is struggling to calm weeks of street protests by Sunni Muslims while his fragile government, split among the Shia majority, Sunnis and ethnic Kurds, is deadlocked in a crisis over power sharing.

The attack on Tuz Khurmato was the fourth suicide bombing in Iraq in a week, including one that killed a Sunni lawmaker in a town where protesters have been calling for Maliki to step down. Al-Qaeda claimed responsibility for that bombing.

Sunni unrest and renewed violence in Iraq is compounding fears that the war in neighboring Syria, where Sunni rebels are battling to topple Shia Iran's ally Bashar al-Assad, will upset Iraq's own fragile sectarian and ethnic mix.